[PATCH 1/1] NFC: llcp: Limit size of SDP URI

[Tyler Hicks]

From: Kees Cook <keescook at chromium.org>

The tlv_len is u8, so we need to limit the size of the SDP URI. Enforce
this both in the NLA policy and in the code that performs the allocation
and copy, to avoid writing past the end of the allocated buffer.

Fixes: d9b8d8e19b073 ("NFC: llcp: Service Name Lookup netlink interface")
Signed-off-by: Kees Cook <keescook at chromium.org>
Signed-off-by: David S. Miller <davem at davemloft.net>

CVE-2018-9518

(cherry picked from commit fe9c842695e26d8116b61b80bfb905356f07834b)
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 net/nfc/llcp_commands.c | 4 ++++
 net/nfc/netlink.c       | 3 ++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
index 1017894807c0..50386f232a46 100644
--- a/net/nfc/llcp_commands.c
+++ b/net/nfc/llcp_commands.c
@@ -151,6 +151,10 @@ struct nfc_llcp_sdp_tlv *nfc_llcp_build_sdreq_tlv(u8 tid, char *uri,
 
 	pr_debug("uri: %s, len: %zu\n", uri, uri_len);
 
+	/* sdreq->tlv_len is u8, takes uri_len, + 3 for header, + 1 for NULL */
+	if (WARN_ON_ONCE(uri_len > U8_MAX - 4))
+		return NULL;
+
 	sdreq = kzalloc(sizeof(struct nfc_llcp_sdp_tlv), GFP_KERNEL);
 	if (sdreq == NULL)
 		return NULL;
diff --git a/net/nfc/netlink.c b/net/nfc/netlink.c
index a9b2342d5253..a00f17fe2a74 100644
--- a/net/nfc/netlink.c
+++ b/net/nfc/netlink.c
@@ -62,7 +62,8 @@ static const struct nla_policy nfc_genl_policy[NFC_ATTR_MAX + 1] = {
 };
 
 static const struct nla_policy nfc_sdp_genl_policy[NFC_SDP_ATTR_MAX + 1] = {
-	[NFC_SDP_ATTR_URI] = { .type = NLA_STRING },
+	[NFC_SDP_ATTR_URI] = { .type = NLA_STRING,
+			       .len = U8_MAX - 4 },
 	[NFC_SDP_ATTR_SAP] = { .type = NLA_U8 },
 };
 
-- 
2.7.4